Standard Communication Target Connection

Using the RJ-11 connector, the MPLAB® ICD 4 In-Circuit Debugger is connected to the target device with the modular interface (six conductor) cable. The pin numbering for the connector is shown from the bottom of the target PCB in Figure 1.

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Cable connections on the debugger and target are mirror images of each other (e.g., pin 1 on one end of the cable is connected to pin 6 on the other end of the cable). See Modular Cable Specification.

FIGURE 1: STANDARD CONNECTION AT TARGET

Target Connection Circuitry

Figure 2 shows the interconnections of the MPLAB ICD 4 In-Circuit Debugger to the connector on the target board. The diagram also shows the wiring from the connector to a device on the target PCB. A pull-up resistor (usually around 50 kΩ) connected from the VPP/MCLR line to the VDD is recommended so that the line may be strobed low to reset the device.

FIGURE 2: STANDARD CONNECTION TARGET CIRCUITRY

Target Power

In the following descriptions, only three lines are active and relevant to core debugger operation: Pins 1 (VPP/MCLR), 5 (PGC), and 4 (PGD). Pins 2 (VDD) and 3 (VSS) are shown on Figure 2 for completeness.

When providing power to the target device, ensure that the target is not exposed to voltages higher than the device VDD rating.

Absolute maximum ratings for the device VDD must not be exceeded. Exposure to the maximum rating conditions for any length of time may affect device reliability.

Functional operation of the device at conditions above the parameters indicated in the device data sheets specification is not recommended. See the device data sheet for required device voltage levels and maximum ratings.

EXTERNALLY POWERED THROUGH TARGET
The recommended method for powering the target device is an external power supply connected directly to the target board. In this configuration, target VDD is sensed by the debugger to allow level translation for the target low-voltage operation. If the debugger does not sense voltage on its VDD line (pin 2 of the interface connector) it will not operate.

EXTERNALLY POWERED THROUGH DEBUGGER
An alternative method of powering the target device is an external power supply connected directly to the MPLAB ICD 4. Be aware that you must also select power from the MPLAB ICD 4 debugger via MPLAB X IDE.

Not all devices have the AVDD and AVSS lines, but if they are present on the target device, all must be connected to the appropriate levels in order for the debugger to operate. They cannot be left floating.

In general, it is recommended that all VDD/AVDD and VSS/AVSS lines be connected to the appropriate levels. Also, devices with a VCAP line (PIC18FXXJMCUs, for example) should be connected to the appropriate capacitor or level.

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The interconnection is very simple. Any problems experienced are often caused by other connections or components on these critical lines that interfere with the operation of the MPLAB ICD 4 In-Circuit Debugger system, as discussed in the following section.

Circuits That Will Prevent the Debugger From Functioning

Figure 3 shows the active debugger lines with some components that will prevent the MPLAB ICD 4 In-Circuit Debugger system from functioning.

FIGURE 3: IMPROPER CIRCUIT COMPONENTS

In particular, these guidelines must be followed:

Do not use pull-ups on PGC/PGD – they could disrupt the voltage levels.

Do not use capacitors on PGC/PGD – they will prevent fast transitions on data and clock lines during programming and debugging communications, and slow programming times.

Do not use capacitors on MCLR – they will prevent fast transitions of VPP. A simple pull-up resistor is generally sufficient.

Do not use diodes on PGC/PGD – they will prevent bidirectional communication between the debugger and the target device.

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